1. Field of the Invention
The present invention relates to a digital image edge enhancement process.
2. Description of the Related Art
Digital images input from a digital camera and the like are subjected to various types of image correction. Various methods are used in the edge enhancement process, which is one of these image correction processes. For example, the edge is determined to be between pixels in the image process disclosed in Japanese Laid-Open Patent No. 5-108823. Furthermore, a threshold value which determines the edge is automatically calculated in the image process disclosed in Japanese Laid-Open Patent 10-143673.
Generally, when enhancing the sharpness of a digital image by an edge enhancement process, it is desirable to adjust the thickness of the edge, i.e., the range of edge enhancement, in accordance with the characteristics of the photographic object. For example, when photographing a building or man-made object, the image appears to have an added border when the line of the contour of the building is thickened, such that the image appears unnatural. Accordingly, it is desirable to enhance the line by narrowing the edge enhancement range so as to not thicken the line in the case of buildings and the like. Conversely, when enhancing an edge by thinning the edge in the case of a human image and the like, the enhancement often produces the opposite effect of making the eyes and the like appear unnatural. For this reason it is desirable to smoothly enhance the edge by broadening the width of the edge in the case of human images. That is, when photographing people, the enhancement range must be somewhat broadened with moderate edge enhancement. Numerous methods of automatic edge enhancement have been proposed heretofore, but the enhancement range must be input manually.